[Pedant warning] I think you'll find the valve should always point to the right. Away from the bike leaning on the side stand [/end of pedant warning] [/font]
Interesting thought.
I actually had to think about which way my valves point and they do, indeed, face away from the side stand.
Although it doesn't make much of a difference to me as such, since, whenever I pump up the tyres, I put the bike on the centre stand and give the wheels a spin to check for any intrusions.